Renal carbonic anhydrase inhibition reduces high altitude sleep periodic breathing

Abstract

The efficacy of carbonic anhydrase (CA) inhibitors in amelioration of periodic breathing during sleep at high altitude is not fully understood. Although CA is present in anumber of tissues, we hypothesized that selective renal CA inhibition without physiologically important inhibition of other tissue CA, may be sufficient alone by its generation of a mild metabolic acidosis to stimulate ventilation and prevent periodic breathing. We studied benzolamide (3 mg/kg), a selective inhibitor of renal CA, in 4 climbers on ventilation and ventilatory responses at sea level and on arterial O 2 saturation (Sa O 2 %) and periodic breathing during sleep at altitude. At sea level, ventilation increased and Pa O 2 rose accompanied by a mild metabolic acidosis. The isocapnic hypoxic ventilatory response was unchanged but the hyperoxic hypercapnic ventilatory response rose 40%. At high altitude (4400 m), daytime Sa O 2 % improved from 81 to 85 and venous plasma HCO 3 fell from 18.9 to 14.8 mM. During sleep, mean Sa O 2 % rose from 76 to 80 and periodic breathing decreased 75%. We conclude that metabolic acidosis occurring with all CA inhibitors is one of the major stimulant actions of these drugs on ventilation while awake and during sleep at high altitude.